Our textbook mentioned that the compound in the diagram racemizes in presence of $\ce{AlCl3}$, but it didn't explain anything. image for compound

Any help regarding the mechanism of the reaction would be appreciated.

  • 2
    $\begingroup$ I think you'll get better results if you specifically ask the question you have, not just stating a situation you don't understand. $\endgroup$
    – Stian
    Nov 17, 2021 at 14:12
  • $\begingroup$ @StianYttervik I just want to know how the reaction proceeds. Was it that difficult to decipher from the post ? $\endgroup$ Nov 17, 2021 at 14:30
  • 1
    $\begingroup$ @HelloWorld1729 Please cite your textbook, use proper compound name ((butan‐2‐yl)benzene), mention conditions and your thoughts on mechanism. Also, please refrain from using MathJax in titles and feel free to check out this page, this page and this one on how to format your posts better with MathJax and Markdown. $\endgroup$
    – andselisk
    Nov 17, 2021 at 14:39

1 Answer 1


A plausible reaction leading to your product is the following reaction:

enter image description here

i.e., a mixture of (R) and (S)-configurated product is formed. In the presence of $\ce{AlCl3}$, the alkylhalogenide becomes something like a carba cation, where you potentially loose stereogenic information (-> racemic mixture). In the work-up, the addition of water destroys [quenches] $\ce{AlCl3}$, thus the forward and backward reaction no longer is catalyzed, and eventually, it is possible to separate the two isomers.

However, if you mix one of the two pure isomers with $\ce{AlCl3}$ (or an other Lewis acid, e.g., $\ce{FeCl3}$ and heat the mixture, you will again generate a mixture of alkylated benzene. (I intentionally use mixture here; because the installation of an alkyl group increases benzene's character as a Lewis base [$\pi$ bonds!], eventually, you might end up with more than one alkyl group installed, too.)

The reversible character of the Friedel-Crafts alkylation may be used to your advantage, though to block e.g., the p-position relative to an already installed substitutent directing in (ortho) and (para)-position, especially with a tert-butyl group.


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